Chemical concepts: Functional Groups, Polarity, Solubility

NU FS 372+373

Key concepts

  1. Remember common functional groups and be able to recognise them in complex organic molecules (slides 3-12)

  2. Understand the concepts of electronegativity and polarity

  3. Understand the principles governing solubility and miscibility

  4. Be able to define log Pow and understand the singificance of log Pow values


Alkanes: CnH2n+2

Formula

Structure

Name / Uses


CH4



Methane - gas used for cooking.


C2H6



Ethane


C3H8



Propane - heating fuel.


C4H10



Butane - lighter / camping fuel.


C5H12



Pentane


C6H14



Hexane


Hydrocarbon Rings:

Formula

Structure

Name / Uses


C6H12



Cyclohexane - a saturated hydrocarbon with the atoms arranged in a hexagonal ring. In organic chemistry, the presence of Hydrogen atoms is often assumed and this compund can be reprsented by a hexagonal ring:




C6H6


Benzene - an industrial solvent.


The Benzine Ring is one of the most important structures in organic chemistry. In reality, its alternate double and single bonds are "spread around" the ring so that the molecule is symetrical. This structure is represented by a hexagon with a circle:



C7H8


Toluene - an important solvent and starter chemical.


Using the Benzine Ring, this molecule can also be depicted as:



C10H8



Naphthalene - used in moth balls. This can be depicted as two fused Benzine Rings:



Alcohols: CnH2n+1OH


eneral ormula

Series Name

Details

Examples

Structures


CnH2n+1OH


Alcohols


Alcohols have the OH

(hydroxyl) group in the molecule.

CH3OH

Methanol

wood alcohol


C2H5OH

Ethanol drinking alcohol


C6H5OH

Phenol carbolic acid - used as disinfectant




Ethers: (CnH2n+1)2O





(CH3)2O






Dimethyl



Ethers have an O atom

Ether

a gas


(CnH2n+1)2O

Ethers

attached to

two hydrocarbon chains (or rings).

(C2H5)2O

Diethyl Ether

a liquid




used as an




anaesthetic)

Aldehydes - CnH2n+1CHO



CnH2n+1CHO


Aldehydes have a CHO group attached to a hydrocarbon chain (or ring).


HCHO H

Formaldehyde preservative in C labs

O

CH3CHO

Acetaldehyde


H


Ketones - (CnH2n+1)2CO



(CnH2n+1)2CO

Ketones have a CO group attached to two hydrocarbon chains (or rings).


CH3COCH3

Dimethyl Ketone Also known as acetone: nail- varnish remover


Carboxylic Acids

C2H5CO2H

(fatty acids for high n): CnH2n+1CO2H



CnH2n+1CO2H


Fatty Acids contain the CO2H (or

COOH) group attached to a hydrocarbon chain or ring.


HCO2H

Formic Acid

in ant bites and stinging nettles


CH3CO2H

Acetic Acid

vinegar


C3H7CO2H

Butyric Acid the rancid butter smell




H3C

Esters:

RCO2R’



RCO2R'


(R, R' are Hydrocarbon chains or rings).

Esters are similar to Fatty Acids except that the H in the COOH group is another hydrocarbon chain. They are usually very sweet smelling liquids used in perfumes.


CH3CO2CH3

Methyl Methoate essence of pear drops


Amines: RCH2n+1NH2



Amines have one or more of the Hydrogen atoms in Ammonia (NH3) replaced by a Hydrocarbon chain or ring.




CnH2n+1NH2

Primary Amines have the formula RNH2


Secondary Amines have the formula RR'NH


CH3NH2

Methylamine

a pungent, water soluble gas


Tertiary Amines have the formula RR'R''N.



(R, R', R'' are

Hydrocarbon chains or rings).


Amino Acids H2NRCO2H



CnH2nNH2COOH

Amino Acids have two functional groups: the amine (HN2) group and the fatty acid (COOH) group.


Amino Acids combine together to form proteins which are an important component of living organisms.


CH2NH2COOH

Glycine

the simplest amino acid.


Amides: RCONH2

Primary Amides

propanamide


,
,

Benzamide



Secondary Amides - have one hydrogen and one alkyl or aryl group on the N of the amide group.


N-methylethanamide,


Tertiary Amides - have two alkyl or aryl groups attached to the N of the amide group.


N,N-dimethylethanamide,

,


(a “dipeptide”)

Chlorophyll a (bluish-green and b yellowish-green)


Visible spectrum

Chlorophyll a and b


methyl

aldehyde


pyrrole

ethyl


ketone


ester


alkyl chain

Intramolecular Bonds


H   H C C

H H

strongly electronegative and electropositive atoms eg. salts

R C O-Na+

Na+Cl-

Electronegativity

Electronegativity is the attraction of an atom for the electron cloud that forms the bond between 2 atoms

Least electronegative element


Pauling Scale

Most electronegative element

Polarity

Arises through differences in electronegativity:


A B

δ+ δ-

A B


A and B have equal electronegativities..

nonpolar bond

+

A

B is more electronegative than A..

polar bond

-

B

B is much more electronegative than A..

ionic bond

Dipole Moment

B is more electronegative than A:

δ+ δ-

d

A B


The product of the magnitude of the charge (δ) either on A or B and the AB bond length (d) is called the dipole moment (µ) of the bond:


µ (AB) = δ x d (SI units are debye (D))

Molecular dipole moments are the vector sum of the dipole moments of all bonds in the molecule

Polar vs. Nonpolar Molecules


H H

H C C H

H H H C C

H

OH

H H H H


Ethane: Non-polar Ethanol: Polar

Functional groups can be classified as electron withdrawing (−I) or electron donating (+I) groups relative to hydrogen

δδδδ+

δδδ+

δδ+

δ+

An electronegative (electron withdrawing) element X not only polarizes the C-X bond but also draws electrons away from more distant bonds to a diminishing extent. This is the inductive effect, occurring through σ bonds.

CH3——CH2——CH2——CH2——X

δ-

<

<

<

<

Inductive Effects


O2N—<<—CH2<—Ph

H——CH2——Ph

NO2 is –I i.e. electron withdrawing; this also draws electrons away from the Ph group in the C--Ph bond

Intermolecular Bonds

H

O δ-

approach each other F

– a type of dipole- dipole interaction.

Dielectric constant


ε > 15 = polar solvent

ε < 15 =nonpolar solvent

Polar vs. Nonpolar Solvents


Non- polar

Polar aprotic

Polar protic

Longer hydrocarbon chain less polarity

**

**

**

Miscibility of Solvents with Water


http://www.sigmaaldrich.com/Area_of_Interest/Research_Essentials/Solvents/Solvents_Site_Map.html

**

** **

Miscibility of Solvents with Hexane


http://www.sigmaaldrich.com/Area_of_Interest/Research_Essentials/Solvents/Solvents_Site_Map.html

Solubility of Alcohols[ CnH2n+1OH ]


R-OH

Boiling Point

°C

Solubility g/100g Water

Methanol

65.5

Ethanol

78.3

1-Propanol

97.0

2-Propanol

82.4

1-Butanol

117.2

7.9

1-Pentanol

137.3

2.3




Solubility of Carboxylic Acids


O

R= R C OH

Boiling Point

°C

Solubility g/100g Water

Solubility g/100g Ethanol

H

101

CH3

118

CH3-CH2-

141

CH3-(CH2)2-

164

CH3-(CH2)3-

187

3.7

Soluble

CH3-(CH2)4-

205

1.0

Soluble

C6H5-

250

0.34

Soluble

CH3-(CH2)10-


Insoluble

100

CH3-(CH2)16-


Insoluble

5.0

A

B

Solvents are H2O and CCl4 Density of CCl4 is 1.59 g/cm3

Solutes are I2 and KMnO4


Which solvent is the upper layer?


Which flask has I2 added ?


http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch15/solut.php

How will the (coloured) compounds partition?



Oil/vinegar mixture

Herb infused oils

Partition Coefficient


log Poctanol/water

= log

log Pow Values

(note: log10(10)=1; log10(1)=0; log10(0.1)= -1; etc)


Compound

log Pow

Methanol

-0.77

2-Propanol

0.5

1-Hexanol

2.03

Benzene

2.13

Limonene

4.57

PCDD/PCDF (polychlorodibenzo- dioxin/furan)

6.5-8.8

CH3

log Pow Values of mostly lipophilic food components


1.87 2.26 3.5 5.1


INCREASING experimental log P values >>>>>>>>

log Pow Values of mostly hydrophilic food components


2.13 -1.85 -1.76 -3.24


DECREASING experimental log P values >>>>>>

Soluble in what ??




Solubility of CO2 in water


Figure 5–Fraction of dissolved carbon dioxide, carbonic acid, bicarbonate, and carbonate in water, as a function of pH (adapted from Daniels and others 1985).

Solubility of CO2 in a can

Henry’s Law:


The solubility of a gas in a liquid is proportional to the pressure of gas above that liquid


Picture from Chemistry Structures of Life, K.Timberlake, 2010

Simple Method for Measurement of CO2 in a food

Figure 6–Example of experimental set-up to measure carbon dioxide content in liquid or solid food, and associated reactions (adapted from Gill 1988).


Measurement of O2 also possible (eg using luminescence sensors) but interactions with the food must be considered)